Why the father of disruption theory is worried about Apple

FORTUNE — About 40 minutes into the interview with Clay Christensen that Asymco‘s Horace Dediu posted Wednesday on his Critical Path podcast, Dediu brings the conversation around to Apple AAPL.

Christensen, who was Dediu’s mentor at Harvard Business School, is best known as the author of The Innovator’s Dilemma — a book that “deeply influenced” Steve Jobs, according to his biographer. It describes how great companies that seem to be doing all the right things — listening to their customers, increasing productivity, using technology to steadily improve their products — almost invariably get overtaken by new, less profitable technologies that for very good business reasons the established leaders don’t pursue until it’s too late.

Christensen had told Andrew Keen in a TechCrunch TV interview earlier in the week that he was “worried” about Apple, but Keen didn’t follow up.

Dediu does. What is it, he asks Christensen, that concerns you?

Christensen, it turns out, has two concerns about Apple:

1. That it’s too much like Sony under Akia Morita when Sony SNE was introducing one hit product after another — portable radios, TVs, tape players, CD players, video recorders, etc. Each was disruptive to the market, but not to Sony itself because the margins they offered were very attractive internally. “I worry that Apple is in the same situation,” he says.
2.That Apple’s integrated product lines are vulnerable to newcomers — like Google GOOG — taking a modular approach. “The transition from proprietary architecture to open, modular architecture just happens over and over again,” he says. “It happened in the personal computer, and although it didn’t kill Apple’s computer business, it relegated them to a minor player.”

Dediu has an answer — sort of — for Christensen’s first concern, pointing out that Apple was willing to cannibalize the iPod with the iPhone, and the Mac with the iPad.

“Apple does have a self-destructive instinct,” Dediu says. However: “It hasn’t been one where they have hurt themselves very much doing it, but rather slowly deprecating their previous successes.”

As for Christensen’s second concern — the threat to Apple’s proprietary, integrated approach — Dediu admits that it’s an issue he’s been “stressing over,” but that it has some interesting twists and turns.

UPDATE: There’s a long profile of Christensen in the current New Yorker (The Innovators Issue, with the cloud on the cover) that does a far better job explaining his theories and their impact on American industry than my brief precis.